The approaches described in this section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section. Furthermore, all embodiments are not necessarily intended to solve all or even any of the problems brought forward in this section.
Audio Class-D drivers may be used in order to provide high powered audio output signal with high efficiency, typically comprised between 80 and 90%.
However, Class-D power stage also provides a lot of electromagnetic noise in the radio band, with particular frequency concentrations. This electromagnetic noise can perturb environment systems.
Electromagnetic interference (EMI) may be reduced by using solenoid inductance filters with concentrated magnetic field. However, such filters are expensive.
Electromagnetic interference (EMI) may also be reduced by using a spread-spectrum clock signal, which can be obtained with a phase locked loop or with a pseudo random noise. The use of a pseudo random noise is for example disclosed in U.S. Pat. No. 6,545,533.
However, the known systems do not permit to control the energy spectrum. As a consequence, noise is added into the audio band and reduces the dynamic range at around 91 dB/96 dB. This can be a main issue for example in case of a system given at 103 dB minimum.
There is a need for improved methods and devices for reduction of electromagnetic noise of audio Class-D drivers.